System and method of unacknowledged network layer service access point identifier (NSAPI) recovery in sub-network dependent convergence protocol (SNDCP) communication

ABSTRACT

A system and method of unacknowledged Network Layer Service Access Point Identifier (NSAPI) recovery in Sub-Network Dependent Convergence Protocol (SNDCP) communication are disclosed herein. The disclosed techniques prevent the loss of data which may result from changing between GPRS/GSM modes in a Class B mobile station (MS).

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from and is related to the followingprior applications: System And Method Of Unacknowledged Network LayerService Access Point Identifier Recovery In Subnetwork DependentConvergence Protocol Communication, U.S. Provisional Application No.60/427,239, filed Nov. 19, 2002; and System And Method Of UnacknowledgedNetwork Layer Service Access Point Identifier Recovery In SubnetworkDependent Convergence Protocol Communication, European PatentApplication No. 02026390.1, filed Nov. 25, 2002. These priorapplications, including the entire written description and drawingfigures, are hereby incorporated into the present application byreference.

BACKGROUND

1. Field of the Technology

The present application relates generally to data communications formobile communication devices. More particularly, the application relatesto unacknowledged Network Layer Service Access Point Identifier (NSAPI)recovery for Sub-Network Dependent Convergence Protocol (SNDCP)communication in General Packet Radio Service (GPRS) networks.

2. Description of the Related Art

A mobile station (MS) may communicate in standardized networks such asGlobal System for Mobile (GSM) or General Packet Radio Service (GPRS)networks. In order to communicate data and voice, a MS may need tooperate in accordance with both GSM and GPRS technologies. A Class B MSis a dual mode MS that can communicate in either GSM mode for voice orin GPRS mode for data—but not in both modes simultaneously. In GPRSmode, a Class B MS depends on protocols layered as a stack; networkinfrastructure nodes have corresponding stacks to thereby enablecommunications between the MS and various nodes and networks. 3^(rd)Generation Partnership Project (3GPP) standard document 24.007 (EuropeanTelecommunications Standards Institute (ETSI) Technical Specification(TS) 124 007 V4.1.0 (2001-12)) section 5.2 describes the GPRS protocolstack architecture diagram. GSM and GPRS share certain lower protocollayers, such as the GSM radio frequency (RF) layer.

GSM and GPRS techniques are known to those skilled in the art, as wellas are some of their deficiencies. One such deficiency is related to theresetting of one of the protocol stack layers, namely, the Logical LinkControl (LLC) layer. GSM standard document 04.464 (ETSI TS 101 351V8.3.0 (2000-03)) section 8.5.3.1 details the negotiation of parameterReset in the LLC. There, it explicitly specifies that the LLC shalldiscard requests pending from layer-3 to logical link entities (LLEs)with no further action.

Unfortunately, important user information may be lost as the LLCdiscards the pending requests. This happens particularly when usingunacknowledged Network Layer Service Access Point Identifier (NSAPI)communication over Sub-network Dependent Convergence Protocol (SNDCP)communications. 3GPP standard document 04.65 (ETSI TS 101 297 V8.2.0(2001-09)) section 5.1.2.1 describes what the GPRS SNDCP layer must dowhen it receives a logical link reset indication (LL.RESET.indication).Note that the standard is very explicit about what the SNDCP should doupon receiving the LL reset indication if the NSAPI is usingacknowledged LLC operation.

The fact that a Class B MS can operate only in one mode at a given time(either GSM or GPRS mode) makes a Class B MS particularly vulnerable tothis LLC reset deficiency. In particular, an LLC reset occurs whenchanging from the GPRS mode to the GSM mode. The process of changingmodes from data to voice and back can occur on many occasions during thenormal use of a MS (e.g. due to network coverage inadequacies),occasionally causing data to be lost within the MS stack over the timeof operation of the MS. The GPRS and GSM standards remain silent on howto recover from adverse effects of such mode changes, resulting in someimplementations of the standard exhibiting data loss at a MS. As theability to communicate data decreases, so does the utility of the MS.The time of operation of the MS can be drastically curtailed byimproperly losing data within the protocol layers of the MS stack.

Accordingly, there remains a need for a system and method ofunacknowledged NSAPI recovery in SNDCP communication that overcomes thelimitations present in the current Class B MSs which cooperate withexisting standards. There remains a further need for a system and methodof unacknowledged NSAPI recovery in SNDCP communication thatsystematically recovers from transitions between GPRS and GSM modes in aClass B MS.

SUMMARY

It is an object to obviate or mitigate at least one disadvantage ofprevious dual mode Global System for Mobile Communications (GSM)/GeneralPacket Radio Service (GPRS) Class B mobile station (MS) techniques. Itis a further object to provide a system and method of unacknowledgedNetwork Layer Service Access Point Identifier (NSAPI) recovery inSub-network Dependent Convergence Protocol (SNDCP) communication that isrobust against GSM/GPRS mode transitions and provides reliablecommunications.

In one illustrative embodiment, a system includes a recovering layer-3module and a layer-2 module. The recovering layer-3 module has aprotocol interface for receiving data and multiplexing the data intorequests; means for tracking outstanding requests to determine thestatus of the requests; request resending means for selectivelyresending outstanding requests upon reception of a layer-2 resetindication; and a layer-2 interface for transmitting the requests andreceiving the layer-2 reset indication. The layer-2 module is connectedto the layer-2 interface of the recovering layer-3 module and has aqueue for queuing the requests received from the layer-3 module; meansfor acknowledging the recovering layer-3 module upon completion of therequests; means for indicating a reset condition to the recoveringlayer-3 module via the layer-2 reset indication of the layer-2interface; and a layer-1 interface for transmitting the data to alayer-1 module. The layer-1 module is connected to the layer-2 modulevia the layer-1 interface for transmitting the data from a firstcomponent of the system to a second component of the system over aphysical layer. Preferably, the above-described system is integratedinto a handheld computing or communicating device.

In another illustrative embodiment, a method of unacknowledged NetworkLayer Service Access Point Identifier (NSAPI) recovery in Sub-networkDependent Convergence Protocol (SNDCP) communications is provided. Themethod may include the steps of detecting a layer-2 reset condition inlayer-3; determining outstanding layer-3 to layer-2 requests forunacknowledged layer-2 communication; and resending outstanding layer-3to layer-2 requests from layer-3 to layer-2. The method may also includeeither or both of the steps of, upon detection of the layer-2 resetcondition in layer-3, setting unacknowledged layer-2 communicationsequence numbers to zero in layer-3 and entering a recovery state inlayer-3 for acknowledged layer-2 communications.

Advantageously, the above techniques may be applied within a GPRS ClassB MS having dual mode (i.e. GPRS and GSM) capabilities. In furtherembodiments, the techniques are applied in a Universal MobileTelecommunications System (UMTS) MS.

Other aspects and features will become apparent to those ordinarilyskilled in the art upon review of the following description of specificembodiments in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the attached figures, wherein:

FIG. 1 illustrates a mobile station (MS) and an infrastructure of anetwork which may incorporate certain aspects of the present invention;

FIG. 2 illustrates the elements of the system of FIG. 1 when embodied asa General Packet Radio Service (GPRS) system;

FIG. 3 illustrates in greater detail a recovering Sub-Network DependentConvergence Protocol (SNDCP) layer and a Logical Link Control (LLC)layer for the system of FIG. 2;

FIG. 4 is a signalling diagram illustrating the timing of communicationsbetween the MS and the infrastructure of FIGS. 2-3;

FIG. 5 is a flowchart illustrating a method of unacknowledged NetworkLayer Service Access Point Identifier (NSAPI) recovery in SNDCPcommunications;

FIG. 6 is a flowchart illustrating another method of unacknowledgedNSAPI recovery in SNDCP communication; and

FIG. 7 is a block diagram illustrating another exemplary embodiment of asystem which may incorporate certain aspects of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention mitigates or obviates at least one disadvantage inprevious Global System for Mobile (GSM)/General Packet Radio Service(GPRS) Class B mobile stations. A preferred system and method to providereliable and robust data communications despite GSM/GPRS modetransitions are described herein, using unacknowledged Network LayerService Access Point Identifier (NSAPI) recovery in Sub-NetworkDependent Convergence Protocol (SNDCP) communications.

FIG. 1 illustrates particular aspects of a mobile station (MS) 10 and aninfrastructure 100 of a network 124. A data application 25 on MS 10features a recovering protocol stack 20 to a corresponding application125 on network 124 via infrastructure 100. In the embodiment of FIG. 1,stack 20 includes 5 layers: a layer-1 21, a layer-2 22, a recoveringlayer-3 23, a protocol layer 24, and an application layer 25. Layer-121, layer-2 22, and layer-3 23 find correspondence in an infrastructurestack 120 of infrastructure 100 which includes a layer-1 121, a layer-2122, and a layer-3 123, respectively. Transceivers 30 and 130 of MS 10and infrastructure 100 ensure that information is appropriatelytransmitted and received over one or more physical communicationchannels (e.g. a wireless communication channel). Protocol layer 24corresponds with the protocol used by network 124 beyond infrastructure100. Application layer 25 corresponds to an application 125 whichoperates on top of network 124.

MS 10 typically operates in a data mode, but occasionally switches to avoice mode and back. Although MS 10 temporarily switches out of the datamode, data application 25 may continue to send data, which networkapplication 125 eventually receives via infrastructure 100. The reasonis the presence of recovering layer-3 23, which ensures that outstandingrequests to layer-2 22 are properly retransmitted when MS 10 returns tothe data mode. In this manner, data is not lost and communications aremade more reliable, even when infrastructure layer-3 123 is configurednot to acknowledge its reception of data from MS 10.

Turning now to FIG. 2, the same elements of the system of FIG. 1 appliedto a GPRS system are shown. Protocol stack 20 of MS 10 includes protocollayer 24 as well as application layer 25, configured as needed on a perprotocol and application basis to correspond with network 124 andnetwork application 125, respectively. Examples of protocol layer 24include Internet Protocol (IP) Version 4 (IPv4), IP Version 6 (IPv6),and X.25; however, many other suitable protocols may be utilized.Examples of MS applications 25 and network applications 125 includee-mail, web browsing, and chat applications, as well as other suitableapplications with a communication component which operates over protocollayer 24 and network 124.

Further down stack 20, layer-1 21 components are illustrated in moredetail. In FIG. 2, layer-1 21 is implemented with three sub-layersincluding a media access control (MAC) 21 a, a radio link control (RLC)21 b, and a GSM radio frequency (RF) 21 c, each finding correspondencewith infrastructure stack sub-layers of infrastructure layer-1 121. Inan alternate embodiment, instead of using the GSM RF sub-layer 21 c inparticular and GSM components of layer-1 21 of FIG. 2 in general,Universal Mobile Telecommunications System (UMTS) layer-1 components andUMTS RF sub-layers are utilized.

Of particular interest, new recovering layer-3 23 of FIG. 2 is embodiedin a recovering Sub-Network Dependent Convergence Protocol (SNDCP). Notethat this is an improvement over traditional SNDCP. Also of interest isa traditional link layer control (LLC) layer-2 22, which providesservices to recovering SNDCP layer-3 23. The structure and co-operationof recovering SNDCP layer-3 23 with LLC layer-2 22 will be described ingreater detail with reference to FIGS. 3 and 4, respectively. Finally,infrastructure 100 of FIG. 2 has stack 120 split into two stacks, withlayer-1 121 implemented in a base station system (BSS) 140, and layer-2122 and layer-3 123 implemented in a serving GPRS support node (SGSN)150.

Turning now to FIG. 3, recovering SNDCP layer-3 and LLC layer-2 stackcomponents of FIG. 2 are shown in more detail. Application 25, such asan e-mail client or wireless access protocol (WAP) browser, usesprotocol 24, such as IP, to send data to a corresponding networkapplication (not shown in FIG. 3). The data is sent in a plurality ofpacket data units (PDUs) 35, which are indexed using a Network LayerService Access Point Identifier (NSAPI) 31. Recovering SNDCP 23(layer-3) multiplexes several NSAPIs into a single “unacknowledged”service access point identifier (UNACK SAPI) 32 provided by LLC 22.

As used herein, unacknowledged communication between a source and adestination is defined to mean that an acknowledgement need not be sentback to the source upon reception of the communication at thedestination. Unacknowledged NSAPI is a term that is meant to includeboth NSAPIs that are configured for unacknowledged communication at a MSsource, and NSAPIs at a MS source which use a SAPI in unacknowledged LLCoperation mode at a MS source (such as an NSAPI that is logically linkedto an LLC SAPI that operates in unacknowledged mode). Thus, asillustrated in FIG. 3, NSAPIs 31 are unacknowledged as they arelogically linked to LLC SAPIs 32 that, as illustrated, operate inunacknowledged mode. Although not expressly shown in FIG. 3, LLC SAPIscan also operate in acknowledged mode and, when so configured, NSAPIslogically linked to acknowledged LLC SAPIs operate as acknowledgedNSAPIs.

Recovering SNDCP 23 sends PDUs 35, each of which is initially bufferedin a PDU queue 27, to LLC 22 in a series of requests 33. PDUs in PDUqueue 27 are considered outstanding until an acknowledgement (ACK) 34 isreceived from LLC 22. 20 Note that ACK 34 is sent when LLC 22 has sentPDU 35, not when the infrastructure has received PDU 35 (as SAPI 32 isunacknowledged). PDUs 35 are sent by LLC 22 via SAPI 39 to the lowerlayers, such as sub-layer radio resource (RR) 40 which is responsiblefor applying encryption parameters 41 and setting up logical channels 42which map to physical channels 43 of transceiver 30. Thus, inunacknowledged NSAPI communication, failure to receive ACK 34 atrecovering SNDCP 23 from LLC 22 indicates that a corresponding request33 has an unconfirmed transmission status. ACK 34 indicates torecovering SNDCP 23 that one or more requests 33 have been transmittedby LLC 22.

When LLC 22 is reset, it sends an LL-RESET.indication (LL-R.i) 38 torecovering SNDCP 23. Possible reasons for receiving LL-R.i 38 include MS10 performing a GSM task and/or suspending GPRS service, or MS 10performing a routing area network update. This results in a resetexchange identification (XID) command being received by LLC 22 after itbuffers one or more SNDCP-to-LLC requests 33 in a request queue 36. Anexample of a GSM task is a location area update by the MS, after whichGPRS service could be suspended even though a GPRS task (e.g. sending ane-mail message) may be being performed.

In accordance with conventional methods, LLC 22 is required to flushqueue 36 without further action immediately prior to sending LL-R.i. 38.Furthermore, upon reception of LL-R.i 38 in unacknowledged operation,the SNDCP is required to: (1) treat all outstanding SNDCP-LLC requesttype primitives as not sent; (2) reset all SNDCP exchange identification(XID) parameters 28 to their default values; and (3) for every NSAPIusing unacknowledged peer-to-peer LLC operation, set the send N-PDUnumber 37 (unacknowledged) to zero (0). The recovery aspect inrecovering SNDCP 23 goes further by resending all outstanding PDUs inqueue 27 after renumbering them in accordance with the newly establishedNPDU number 37 sequence starting with zero. Thus, without the recoveringaspect of recovering SNDCP 28, the outstanding PDUs either never getsent or get sent with improper sequence numbers. SNDCP-to-LLC requestscan include LLC XID requests as well as PDUs.

Referring now to FIG. 4, a signaling diagram illustrating the timing ofcommunications between MS stack 20 and infrastructure 100 of FIGS. 2-3is shown. In FIG. 4, time flows generally from top to bottom. MS 10 isinitially operating in a GPRS mode 255. Protocol layer 24 sends data 210to recovering SNDCP 23. Data 210 is protocol and application dependent,and is configured to operate on network 124 and with network application125 (FIG. 2).

Recovering SNDCP 23 transmits data 210 to LLC 22 in a series ofrequests, such as a REQ 1 220, which are queued 230 as required. Eachqueued request has a send N-PDU sequence number, illustrated as (n-1)for queued request 235 which corresponds to REQ 1 220. LLC 22 transmitssuch queued requests via PDUs, such as a PDU 240, which corresponds toqueued request 235. Upon completion of the transmission, LLC 22 sends anACK-1 250 back to recovering SNDCP 23. Note that ACK-1 250 was not sentfrom SGSN 150, but rather originated from LLC 22 thereby illustratingthat PDU 240 was sent using unacknowledged NSAPI. Also note that PDU 240was sent while MS 10 was operating in GPRS mode 255.

At some point in time before all of data 210 has been sent as PDUs toSGSN 150 indicated by a dotted line 260, MS 10 changes its operatingmode from GPRS mode 255 to a GSM mode 265. One or more subsequentrequests 270 made by recovering SNDCP 23 to LLC 22 become queued 280.Each queued request in GSM mode 265, including a queued request 285corresponding to request REQ 2 270, cannot be sent. While recoveringSNDCP 23 waits for an acknowledgement from LLC 22, LLC 22 receives anLL-RESET 290 from SGSN 150. In response to LL-RESET 290, LLC 22 isrequired to flush queue 300 without taking further action. With an emptyqueue 310, LLC 22 is required to send an LL-RESET.indication 320 torecovering SNDCP 23.

Upon reception of LL-RESET.indication 320, recovering SNDCP 23 istraditionally required to perform steps 330 through 360. At step 330,recovering SNDCP 23 treats all outstanding SNDCP-LLC request typeprimitives as not sent; at step 340 recovering SNDCP resets all SNDCPXID parameters to their default values; at step 350 recovering SNDCP 23sets the send N-PDU number 37 (unacknowledged) to zero (0) for everyNSAPI using unacknowledged peer-to-peer LLC operation; and ifacknowledged communication is also supported by recovering SNDCP 23 atstep 360, for every NSAPI using acknowledged peer-to-peer LLC operation,enter the recovery state and suspend the transmission of SN-PDUs untilan SNSM-SEQUENCE.indication primitive is received for the NSAPI.

Recovering SNDCP 23 also performs a non-traditional step 370 at whichrecovering SNDCP 23 resends unacknowledged NSAPI requests which areoutstanding. This is done using the new sequence numbers for the sendPDUs after performing step 350. Step 370 ensures that the PDUs do notremain in recovering SNDCP 23, thereby ensuring that they no longer takeup memory. After step 370, recovering SNDCP 23 recovers from the adverseeffects of LL-RESET 290 at LLC 22: a request REQ 2 380 recovers whereREQ 2 270 failed. When LLC 22 queues 390 the resent request REQ 2 380, aqueued request 395 now contains the correct sequence number (0) whereasthe previous queued request 285 corresponding to REQ 2 270 contained thewrong sequence number (n).

At some point at a time 400, MS 10 returns from operating in GSM mode265 to operate again in a GPRS mode 405. After time 400, PDUs 410corresponding to queued requests 395 are sent by LLC 22 to SGSN 150,thereby completing the transmission of data 210 from MS 10 to SGSN 150,which then transmits data 430 to network 124.

Referring to FIG. 5, a flowchart for a method of unacknowledged NSAPIrecovery for SNDCP communication is shown. At step 410 of FIG. 5, anLL-RESET.indicator from the LLC is identified at the recovering SNDCP.At step 420, the recovering SNDCP identifies any outstandingunacknowledged NSAPI requests which have been sent to the LLC by therecovering SNDCP, but not acknowledged by the LLC. At step 350, for eachunacknowledged NSAPI, the recovering SNDCP sets the N-PDU sequencenumber to zero. At step 370, the recovering SNDCP resends theoutstanding unacknowledged NSAPI requests using the new N-PDU sequencenumbers set at step 350 to start each outstanding request sequence.

Referring to FIG. 6, a flowchart for another exemplary method ofunacknowledged NSAPI recovery for SNDCP communication is shown. At step610, an LL-RESET command is received at an LLC in an MS. At step 620,all LLC XID parameters are reset to their default values. At step 630,all requests that are pending from a layer-3 communication layer to aplurality of LLEs are discarded. At step 640, a logical link resetindication (LL-RESET.indication) is received at an SNDCP from the LLC.In response to the LL-RESET-indication all SNDCP XID parameters arereset to their default values at step 650. In addition, at step 660 itis determined whether the NSAPI currently being processed isunacknowledged. If the NSAPI is unacknowledged, then steps 670 and 680ensue whereas step 690 ensues otherwise. At step 670, for every NSAPIusing unacknowledged peer-to-peer LLC operation, a sequence number ofthe next network packet data unit (N-PDU) is set to zero. At step 680,if the NSAPI is using unacknowledged peer-to-peer LLC operation,outstanding SNDCP-to-LLC requests are transmitted to the LLC. At step690, for every NSAPI using acknowledged peer-to-peer LLC operation, therecovery state is entered and the transmission of SN-PDUs is suspendeduntil an SNSM-SEQUENCE.indication primitive is received for the NSAPI.At step 695 it is determined if all NSAPIs have been processed and, ifnot, the next NSAPI is taken thru steps which follow step 650.

FIG. 7 is a block diagram illustrating another embodiment of anexemplary system which may incorporate aspects of the present invention.A system 700 includes a recovering layer-3 module 730 connected via alayer-2 interface 760 to a layer-2 module 770. Layer-2 module 770 isconnected via a layer-1 interface 840 to a layer-1 module 850.Recovering layer-3 module 730 has a protocol interface 720 for receivingdata 710 and multiplexing the data 710 into requests 740. Recoveringlayer-3 module 730 also has an outstanding request tracking component750 to determine the status of the requests and selectively resendingoutstanding requests 830 upon reception of a layer-2 reset 820indication. Layer-2 interface 760 is used for transmitting requests 740,830 and for receiving layer-2 reset indication 820.

Layer-2 module 770 has a queue 790 for queuing requests 780 receivedfrom layer-3 module 730. Layer-2 module 770 ordinarily acknowledges 810recovering layer-3 module 730 upon completion 800 of requests 780.Layer-2 module 770 also indicates when a reset condition occurs torecovering layer-3 module 730 via layer-2 reset indication 820.Typically, when a reset condition occurs, queue 790 is flushed;therefore recovering layer-3 module 730, upon detection of resetcondition 820, resends any outstanding requests 830 which have not beenacknowledged by layer-2 module 770. Layer-1 module 850 is connected tolayer-2 module 850 via layer-1 interface 840 for transmitting data 710from a first component of a larger system, such as system 700, to asecond component of a larger system (not shown) over a physical layer.

As apparent, the above-described methods and systems mitigate the lossof data resulting from transitions between the GSM/GPRS modes in a ClassB MS. The above-described embodiments of the invention are intended tobe examples only. Alterations, modifications, and variations may beeffected to the particular embodiments by those of skill in the artwithout departing from the scope of the invention, which is definedsolely by the claims appended hereto.

1. A method, comprising: receiving a reset exchange identification (XID)command at a Logical Link Control (LLC) of a mobile station (MS);resetting all LLC XID parameters to their default values; discarding allrequests that are pending from a layer-3 communication layer to aplurality of logical link entities (LLEs); receiving a logical linkreset indication (LL-RESET-indication) from the LLC at a Sub-NetworkDependent Convergence Protocol (SNDCP) layer; and upon receipt of theLL-RESET-indication, the performing the following acts at the SNDCP:resetting all SNDCP XID parameters to their default values; for everynetwork service access point identifier (NSAPI) using unacknowledgedpeer-to-peer LLC operation, setting a sequence number of the nextnetwork packet data unit (N-PDU) to be sent by the SNDCP to zero; if theNSAPI is using unacknowledged peer-to-peer LLC operation, then:transmitting outstanding SNDCP-to-LLC requests to the LLC.
 2. The methodof claim 1, comprising the further acts of: before receiving the XIDcommand: performing a GSM task; suspending GPRS service; and bufferingthe one or more SNDCP-to-LLC requests in the LLC.
 3. The method of claim2, comprising the further acts of: performing a routing area networkupdate, thereby resulting in the reset XID command being received by theLLC after the buffering by the LLC of the one or more SNDCP-to-LLCrequests.
 4. The method of claim 2, wherein the act of performing a GSMtask comprises performing a MS location area update, the method furthercomprising the act of: performing a GPRS task by the MS after suspendingthe GPRS service.
 5. The method of claim 2, wherein the GPRS taskcomprises sending an electronic mail (e-mail) message.
 6. The method ofclaim 1, wherein the SNDCP-to-LLC requests include logical link unitdata requests.
 7. The method of claim 1, wherein the SNDCP-to-LLCrequests comprise logical link XID requests.
 8. A method of resettingSub-Network Dependent Convergence Protocol (SNDCP) reset exchangeidentification (XID) parameters, initializing SNDCP unacknowledgedNetwork Service Access Point Identifier (NSAPI) network packet data unit(N-PDU) numbers, and recovering outstanding unacknowledged NSAPIrequests, comprising the acts of: receiving, from a Logical Link Control(LLC) layer, a logical link reset indication (LL-RESET-indication) atthe SNDCP; upon receipt of the LL-RESET-indication, the performing thefollowing acts at the SNDCP: resetting all SNDCP XID parameters to theirdefault values; for every network service access point identifier(NSAPI) using unacknowledged peer-to-peer LLC operation, setting asequence number of the next N-PDU to be sent by the SNOOP to zero; andif the NSAPI is using unacknowledged peer-to-peer LLC operation:transmitting outstanding SNDCP-to-LLC requests to the LLC.
 9. A methodof layer-2 recovery comprising the acts of: identifying a layer-2 resetcondition in layer-3; after identifying the layer-2 reset condition,identifying outstanding layer-3 to layer-2 requests for unacknowledgedlayer-2 communication; and resending outstanding layer-3 to layer-2requests from layer-3 to layer-2; upon identifying the reset conditionin layer-3; setting unacknowledged layer-2 communication sequencenumbers to zero in layer-3; and entering a recovery state in layer-3 foracknowledged layer-2 communications.
 10. A mobile station, comprising: areceiver; a transmitter; an antenna coupled to the receiver and thetransmitter; one or more processors including: a layer-2 module whichinterfaces with the receiver and the transmitter; a layer-3 module whichinterfaces with the layer-2 module; the layer-3 module being operativeto facilitate data communication for the mobile station by sending aplurality of requests to a queue of the layer-2 module, each requestbeing a type that is acknowledged by the layer-2 module butunacknowledged by a destination node; and the layer-3 module beingfurther operative to resend one or more requests that are unacknowledgedby the layer-2 module in response to a reset indication; the layer-3module being further operative to set, in response to the resetindication at the layer-3 module, a packet data unit (PDU number to zerofor use in resending the one or more requests.
 11. The mobile station ofclaim 10, wherein the requests comprise unacknowledged Network LayerService Access Point Identifier (NSAPI) requests.
 12. The mobile stationof claim 10, further comprising: the layer-2 module comprising a LogicalLink Control (LLC) layer; and the layer-3 module comprising a recoveringSub-Network Dependent Convergence Protocol (SNDCP) layer.
 13. A methodof communicating data comprising: facilitating data communication bysending a plurality of requests from a layer-3 module to a queue of alayer-2 module, each request being a type that is acknowledged by thelayer-2 module but unacknowledged by a destination node; and in responseto a reset indication, resending one or more requests that areunacknowledged by the layer-2 module; in response to the resetindication at the layer-3 module, setting a packet data unit (PDU numberto zero for use in resending the one or more requests.
 14. The method ofclaim 13, wherein the requests comprise unacknowledged Network LayerService Access Point Identifier (NSAPI) requests.
 15. The method ofclaim 13, wherein the layer-2 module comprises a Logical Link Control(LLC) layer and the layer-3 module comprises a recovering Sub-NetworkDependent Convergence Protocol (SNDCP) layer.